1. Field of the Invention
This invention concerns cooling fan motors mounted in various kinds of electronic equipment that require heat radiation treatment, such as high performance CPU integrated circuits like microprocessors or IC circuit boards mounted in PCs (personal computers), and improvement of small, flat brushless motors suited to use in such cooling fan motors.
2. Description of the Related Art
As portable telephones, portable PCs and other kinds of electronic equipment have become smaller and more compact in recent years, various parts used within such equipment have necessarily become miniaturized. Electronics technology and semiconductor integration technology have undergone remarkable development in the fields of portable terminals for business mobile computing, desktop PCs, FAX machines, printers and other office automation equipment, drive and control devices for factory automation equipment including precision machining equipment and small industrial robots and so on, and this trend of miniaturization can be expected to continue to accelerate.
However, the biggest obstacle to further downsizing of this portable equipment is the increased heat density of electronic circuits and internal elements such as semiconductors. That is, the increased volume of heat per unit-time, or heat wattage, within the equipment constitutes a major, urgent problem to be resolved in order for higher performance CPU integrated circuits to continue to perform vigorous operations.
With the goal of resolving the CPU heat problem raised by this miniaturization and densification, numerous manufacturers have entered the marketplace with small cooling fans, cooling pipes, heat radiation fins, electronic cooling elements and various other cooling devices and parts that can withstand the rise of temperatures within equipment. All of these have provided some degree of cooling capacity, but their size has not been as small as desired. They have not been of a size suited to portable electronic equipment with the smallness, lightness and portability required of the very thin, notebook-sized personal computers of recent years.
For example, notebook PC models with the most advanced high-performance CPUs of 600 MHz or more that are now on the market have adopted what is called the “interflap system” to efficiently cool the CPU and the personal computer itself. In this, when the liquid crystal display is opened, the rear of the personal computer itself is tilted up to form a space below it, and air is pulled in by a large fan motor mounted in a tunnel-shaped “inter-cooler diecast” and blown from right to left across the CPU surface, then forcefully exhausted along with the heat from within the PC.
When viewed in the direction of the thickness, however, for space reasons this is done by putting a large fan mechanism in another location, offset from a position on the CPU. This is excellent from the perspective of efficient cooling of the PC as a whole, but it is of course not a structure that can cope with slimmed down equipment.
Because the light and slim bodies of the latest notebook personal computers do not have installation space, particularly in the direction of the thickness of the case, countermeasures against heat are an important problem in terms of taking advantage of the capabilities of high-performance CPUs. A very thin, high-efficiency fan mechanism that directly cools CPU parts has become indispensable for future high-performance notebook models.
The Japanese Design Patent 1057608, submitted earlier by the present inventors, can be mentioned as an example of a conventional thin fan motor. This thin fan motor with attached heat sink 200, as shown in FIG. 5 (which differs from the actual outward appearance in order to explain the internal structure) and FIG. 6, is constituted as follows. There is a heat plate 34 fixed to various heat-producing pieces of equipment that require the radiation of heat. This heat plate 34 has a fan motor rotor section roughly in its center. Multiple heat radiation blocks 32a, 32b . . . that rise from the inner surface of the heat plate 34 are lined up radially in a circle centered on the rotational axis of the rotors outside the reach of the rotor blades 30a, 30b . . . The outer periphery has openings as outlets for the moving air. The radiation blocks 32a, 32b . . . are covered by a polymer sheet 24 of the circuit board 22, which is fixed in place by fittings (part D) that engage the corner walls of the heat plate 34, and the air set in motion the rotor fan forcefully cool the heat radiation blocks 32a, 32b . . . The rotor blades 30a, 30b . . . make up a rotor fan 30, which is supported by a magnet yoke 29 on a shaft 33. The shaft 33 communicates with a bearing 27, which is in contact with a spacer 26 and a thrust bearing 25, which is adjacent to a suction yoke 21.
In this thin fan motor with heat sink attached 200, although the heat radiation blocks 32a, 32b . . . are set just outside the reach of the rotor blades 30a, 30b . . . , the stator coil 23 and the rotor magnets 28 are concentrated on the central axis area, and because of the necessity of assuring rotating space for the rotor blades 30a, 30b . . . at the outer edge and the limit on the width measurement to which the heat radiation blocks 32a, 32b . . . can rise, there is a limit to how thin the overall thickness of the fan motor can be and still allow an adequate volume of air.
Because the heat radiation blocks 32a, 32b . . . are of nearly fixed thickness at points in a circle centered on the rotating axis of the fan motor and are lined up in a ring, there is some resistance when the moving air strikes the heat radiation block 32a, 32b . . . and the air does not exit smoothly. And because the rotor blades 30a, 30b . . . are small in blade area, they have little capacity to move air. Therefore, the available cooling effect is not as great as expected.
One other factor is the structural relationship of the rotor fan 30 and the air intake 40 in the side cross section shown in FIG. 6. That is, the structural relationship between the size of the blade area (30a, 30b . . . ) of the rotor fan 30 and the opening of the air intake 40 will limit the air movement capacity during rotation, and the lack of air volume will have a great effect on the performance. The major factor is that, as stated above, there is some resistance when the moving air strikes the heat radiation block 32a, 32b . . . and the air does not exit smoothly. However, what is required is overall redesign of the rotor to provide high efficiency, and reconsideration of the shape and layout of the heat radiation blocks, as well as reconsideration of the structure combining those elements.